Tyre comprising hydrothermally carbonized lignin

ABSTRACT

The invention relates to a pneumatic tire for a vehicle a method for manufacturing such tire, wherein the tire comprises a metal component, a textile component and a cured rubber based component bonded together by means of curing, and wherein the cured rubber based component comprises lignin that has been treated by hydrothermal carbonization. The invention further relates to use of lignin that has been treated by hydrothermal carbonization in a rubber based component of a pneumatic tire.

PRIORITY

This application is a U.S. national application of the internationalapplication number PCT/EP2017/060363 filed on May 2, 2017 and claimingpriority of European patent application number 16397514.7 filed on May9, 2016, the contents of all of which are incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to a pneumatic tyre for a vehicle, the pneumatictyre comprising a rubber based component comprising lignin that has beentreated by hydrothermal carbonization, to a method for manufacturingsuch a tyre and to use of lignin that has been treated by hydrothermalcarbonization in a pneumatic tyre for a vehicle.

BACKGROUND

A pneumatic tyre may be used in various types of vehicles andautomobiles. A pneumatic tyre, once mounted on a rim and inflated, iscapable to absorb shocks when moving over uneven road. An inflatedpneumatic tyre mounted under a vehicle thus serves as an inflatablecushioning for a vehicle.

Approximately close to a billion pneumatic tyres are manufacturedannually in the world. A pneumatic tyre typically comprises a variety ofdifferent materials, such as rubber based components. Rubber basedcomponents typically join various tyre materials together, when the tyreis cured during the tyre manufacturing process. A rubber based componentof a pneumatic tyre typically comprises natural rubber and/or syntheticrubber. The rubber is typically mixed with carbon black in order toobtain rubber having higher reinforcement characteristics.

Each tyre component can be designed for a dedicated purpose. Forexample, tread area components of a pneumatic tyre, which typically arein contact with the road, may require different characteristics thannon-tread area components of the tyre. The composition of the rubberbased component therefore plays a role in the viscoelastic andmechanical performance of the tyre. The amount and type of materialsused in the composition of the rubber based component may have an effecte.g. on traction, tread wear and rolling resistance of the tyre.

Rolling resistance refers to deformation of the tyre, when the tyre isrotating and is in contact with the road surface. The resistance is to alarge extent due to the viscoelastic behavior of the tyre. Rollingresistance accounts for a considerable proportion of fuel consumption infuel-driven vehicles. Rolling resistance also plays a role in the energyconsumption of other types of vehicles, such as those using hybridtechnologies or electricity. Traction and tread wear are performanceparameters which also affect the behavior and durability of the tyre.While traction is typically desirable, the tread wear and rollingresistance of the tyre are not desirable. The tyre performanceoptimization thus form a challenge, since the optimization of oneparameter often may lead to negative results in other desiredcharacteristics.

Tyre characteristics such as durability, reinforcing effect orviscoelastic behavior, are related to the proportion of filler materialsin the rubber based components, such as carbon black. A pneumatic tyremay comprise high amounts of carbon black as reinforcing fillermaterial, such as up to 40 wt. % or more. One of the most common uses ofcarbon black nowadays is as a pigment and reinforcing filler material inautomobile tyres. Carbon black consists mostly of elemental carbon.Carbon black is typically manufactured from fossile carbon sources.Rubber-grade carbon black is typically manufactured in specific grades,each grade having defined characteristics, such as size distribution andspecific surface area according to ASTM standard D1765-14. The finalcharacteristics of a tyre are determined from a cured tyre. Curing istypically done by vulcanization means.

Rolling resistance may be reduced by adding inorganic filler material,such as silica, into the rubber based components located on the treadarea of the tyre. Silica (SiO₂) is a chemical compound, which exists invarious grades and forms, for example as precipitated silica.

Conventional filler materials such as carbon black and silica, when usedas such, are relatively inert. Carbon black interacts in the rubberbased component mainly by means of physical interactions. Silica on theother hand, only interacts once bound into the tyre component by meansof a silane based coupling agent.

Conventional tyre materials pose many challenges. Tyre manufacturingindustry is a major consumer of materials used in rubber basedcomponents. A pneumatic tyre may comprise equal to or more than 80 wt. %of rubber based components, when calculated of the total weight of thetyre. The extensive use of material originating from fossile carbonsources in a tyre is a problem. The complex material composition oftraditional tyres makes them difficult to recycle. The tyre rubbermanufacturing process may involve the use of hazardous material, forexample to increase stiffness of the rubber component. Silica isrelatively expensive. Despite of the use of silica, the conventionalfiller materials still cause considerable amounts of heat generation andflexing fatigue of a tyre, when the tyre is used, which is undesirable.

Rapidly emerging environmental aspects, such as fuel consumption andnoise level reduction efforts in the automobile industry, set newrequirements also to tyre manufacturers. The renewability requirementsand environmental aspects of a tyre play an increasingly important rolein the selection of tyre raw materials. There is a need to produce tyreshaving improved performance characteristics and better environmentalsustainability.

SUMMARY

Some versions relate to a pneumatic tyre for a vehicle, wherein thepneumatic tyre comprises lignin that has been treated by hydrothermalcarbonization. Some versions relate to a method for manufacturing apneumatic tyre for a vehicle, wherein the pneumatic tyre compriseslignin that has been treated by hydrothermal carbonization. Someversions relate to use of lignin that has been treated by hydrothermalcarbonization in a pneumatic tyre for a vehicle.

Lignin is renewable and environmentally sustainable raw material, whichmay be converted into material suitable for pneumatic tyres. Lignincontaining material is easily available for industrial purposes in largequantities. Lignin is a major by-product of the pulp and paper industry.Paper is manufactured from softwood and hardwood, which containsignificant amounts of lignin. A typical example of lignin containingmaterial is spent liquor from biomass fractionation, such as pulp millblack liquor. Agricultural crop residue is another example of lignincontaining material.

Lignin in general contains relatively high amounts of functional groups.Lignin contains functional groups, which may participate in chemicalreactions and form chemical bonds. Functional groups typically presentin lignin comprise, for example, carbonyl groups, aliphatic hydroxylgroups and phenolic hydroxyl groups. Functional groups of lignin aredetectable even after a chemical pulping process, in black liquor. Thefurther processing of lignin containing material, particularly of ligninoriginating from wood, therefore is environmental and cost-effective wayof providing lignin derivatives with functional properties, which may beused as a source of renewable raw material for a pneumatic tyre.

A hydrothermal carbonization treatment of lignin refers to athermochemical conversion process of lignin containing material in anaqueous suspension. Hydrothermal carbonization treatment of ligninproduces lignin derivatives having high carbon content and functionalgroups. Lignin that has been treated by hydrothermal carbonization,hereafter denoted as HTC lignin, provides a cost-effective means forimproving tyre performance. Lignin that has been treated by hydrothermalcarbonization may comprise lignin of wooden origin. HTC ligninoriginating from softwood such as spruce or pine has been found tocontain a particularly suitable molecular structure, which can improvethe characteristics of rubber based components of a pneumatic tyre. HTClignin in a rubber based component of a pneumatic tyre can improve theenvironmental sustainability of the pneumatic tyre.

HTC lignin may be mixed with rubber compounds typically used in the tyreindustry, such as natural rubber, polybutadiene rubber,styrene-butadiene rubber and/or polyisoprene rubber, to manufacture arubber composition. HTC lignin contains surface active functionalgroups. HTC lignin may be configured to form chemical bonds with othercompounds present in the rubber composition. A rubber based componentcomprising HTC lignin may thus be configured to comprise specificcharacteristics. HTC lignin may used to select the characteristics of arubber composition, such that a tyre component with improved performancemay be manufactured. HTC lignin may thus be arranged to improve theperformance of a pneumatic tyre.

HTC lignin may be arranged to comprise, for example, carbon content,surface chemistry, particle size, particle size distribution and/ormorphology of the particle, which are suitable for a rubber basedcomponent of a pneumatic tyre.

Hydrothermal carbonization treatment of lignin has the effect offragmenting the lignin molecular structure. In general, the specificsurface area of HTC lignin may be in the range of 10-150 m²/g, whenmeasured according to ASTM D-6556-10 after the hydrothermalcarbonization treatment from material which has not been mixed withrubber, referred to as virgin material. In general, the oil absorptionnumber of HTC lignin may be in the range of 60-130 ml/100 g, whenmeasured according to ASTM D2414-09 after the hydrothermal carbonizationtreatment from material which has not been mixed with rubber, referredto as virgin material.

Hydrothermal carbonization treatment of lignin has the effect ofincreasing the carbon content of lignin containing material. HTC ligninhas a high carbon content, typically 40 wt. % or more, such as in therange of 40 to 65 wt. %, or even higher.

Hydrothermal carbonization treatment of lignin may be arranged topreserve functional groups of lignin. HTC lignin may thus comprisefunctional groups which are capable of bonding in a chemical reactionwith other compounds present in a rubber composition of a pneumatictyre, as disclosed above. HTC lignin has capability to both physicalinteractions and chemical bonding in a rubber based component of apneumatic tyre. HTC lignin may be arranged to have a molecular structuresuitable for both physical and chemical interactions within a rubberbased component of a pneumatic tyre. HTC lignin which has capability toboth physical interactions and chemical bonding may be used to improveperformance characteristics of a pneumatic tyre.

Hydrothermal carbonization treatment of lignin has the effect ofproducing lignin derivatives with distinguishable characteristics. Themolecular structure of HTC lignin differs from conventional materialsused in rubber based components of a tyre, such as carbon black orsilica. Hydrothermal carbonization treatment of lignin may be arrangedto produce HTC lignin containing carbolic acid functionality, such as2-methoxyphenolic functionality. HTC lignin containing 2-methoxyphenolicfunctionality may in particular be produced from lignin of softwoodorigin. Analytical methods may be used to determine the presence oflignin derivatives in a cured rubber component of a pneumatic tyre.Analytical method suitable for determination of presence of a ligninderivative in a cured rubber component of a pneumatic tyre are, forexample, Pyrolysis-Gas Chromatography/Mass Spectroscopy (GC/MS)analysis, Pyrolysis-Fourier transform infrared spectroscopy (pyro-FTIR)analysis, thermogravimetric analysis or a combination of these, to namea few. For example, a cured rubber based component of a pneumatic tyrethat contains HTC lignin may be pyrolyzed, thereby producing materialreferred to as a pyrolysis product. Suitable pyrolysis temperature maybe about 550° C., when performed according to standard ASTM D3452-06.Pyrolysis-Gas Chromatography/Mass Spectroscopy analysis may be used as ameans to determine the presence of a distinct compound or derivative inthe HTC lignin, such as 2-methoxyphenol. The pyrolysis product may befurther analyzed by means of Pyrolysis-Fourier transform infraredspectroscopy, the method detecting absorption peak ranges and intensitylevels specific to HTC lignin comprising functional groups.

HTC lignin suitable for a rubber based component of a pneumatic tyreacts differently in specific surface area analysis, when compared to acured rubber based component comprising only silica and/or carbon black,when determined by multipoint nitrogen adsorption according to ASTMD6556-10. When pyrolysed at 600° C., a cured rubber based componentcomprising HTC lignin produces a pyrolysis product having a highersurface area than cured rubber based component comprising only silicaand/or carbon black, which would typically be used for the same purposein a pneumatic tyre.

Tangent delta value denotes a ratio of loss to storage modulus, which iscommonly used to describe the rolling resistance of a tyre. Experimentaltest results demonstrate that HTC lignin may be used to reduce the heatgeneration and flexing fatigue of a pneumatic tyre. A cured rubber basedcomponent of a pneumatic tyre comprising HTC lignin may have a lowertangent delta value than a cured rubber based component comprisingeither carbon black or silica. HTC lignin may be used to reduce the heatgeneration and flexing fatigue of a pneumatic tyre with or without asilane based coupling agent. A rubber based component of a pneumatictyre containing HTC lignin with 2-methoxyphenolic functionality has beenobserved to be particularly suitable for reducing the tangent delta,heat generation and/or flexing fatigue of the pneumatic tyre.

The elasticity of a cured rubber based compound is commonly analyzed bymeans of a 300% modulus test. The 300% modulus test refers to a methodfor determining the stress in megapascals (Mpa) required to produce a300% elongation of a sample in a uniaxial tension test. Experimentaltest results demonstrate that a cured rubber based component comprisingHTC lignin may be used to improve the reinforcing capability of apneumatic tyre. A cured rubber based component of a pneumatic tyrecomprising HTC lignin may have a higher modulus value (300% modulustest) than cured rubber based component comprising carbon black. A curedrubber based component of a pneumatic tyre comprising HTC lignin has asignificantly higher modulus value (300% modulus) than a cured rubberbased component comprising lignin which has not been treated byhydrothermal carbonization. Such lignin refers to e.g. lignin present ina pulp mill black liquor.

HTC lignin is ecologically sustainable raw material. HTC lignin may beused as renewable raw material in a rubber based component of apneumatic tyre. HTC lignin may act as a reinforcing agent in a rubberbased composition of a pneumatic tyre. HTC lignin may be used to reduceor replace the amount of conventional carbon black in a pneumatic tyre.HTC lignin may be used to reduce or replace silica in a pneumatic tyre.A rubber based component comprising HTC lignin thus provides means toreduce the content of fossile carbon based materials in a pneumatictyre.

A rubber based component comprising HTC lignin is capable to improve thecharacteristics and performance of the pneumatic tyre. A rubber basedcomponent comprising HTC lignin suitable for reducing the rollingresistance of a pneumatic tyre. A rubber based component comprising HTClignin is particularly suitable for reducing the rolling resistance of apneumatic tyre, when the rubber based component comprises HTC lignin inamounts equal to or higher than 10% by weight of the rubber basedcomponent. The rubber based component may be a tread area component or anon-tread area component of the pneumatic tyre. A non-tread areacomponent refers to e.g. a sidewall area component or a bead areacomponent of a pneumatic tyre.

A rubber based component of a pneumatic tyre may comprise HTC ligninbonded to a rubber compound by means of chemical bonds as well as bymeans of physical interactions. A rubber based component of a pneumatictyre may comprise HTC lignin which has been reacted with a methylenedonor compound. When HTC lignin is used together with a methylene donorcompound in a rubber based component of a pneumatic tyre, thecombination acts as a hardening agent capable of forming networkstructures. A combination of HTC lignin and methylene donor may be usedto increase the stiffness of a cured rubber based component of apneumatic tyre. Such combination may be used to replace phenolic resins.Phenolic resins typically used in rubber compounds provide methylenebridge linkages, when interacting with a methylene donor compound.Phenolic resins typically used in rubber compounds are hazardousmaterial. A rubber based component comprising HTC lignin thus providesmeans to reduce the content of phenolic resins in a tyre.

According to a first aspect, there is provided a pneumatic tyre for avehicle, the tyre comprising a metal component, a textile component anda cured rubber based component, wherein the components have been bondedtogether by means of curing and the cured rubber based componentcomprises lignin that has been treated by hydrothermal carbonization.

According to a second aspect, there is provided a method formanufacturing a pneumatic tyre for a vehicle, the method comprising

-   -   receiving a rubber based component comprising lignin that has        been treated by hydrothermal carbonization,    -   arranging the rubber based component onto a building drum to        form a tubular preform,    -   expanding the tubular preform to form a preform of a pneumatic        tyre,    -   arranging a metal component and a textile component onto the        preform of a tyre, thereby manufacturing a preform of a        pneumatic tyre comprising the rubber based component comprising        lignin that has been treated by hydrothermal carbonization, the        metal component and the textile component, and    -   curing the preform of a pneumatic tyre, thereby bonding the        components together by means of curing and thereby manufacturing        the pneumatic tyre for a vehicle, the tyre thereby comprising a        cured rubber based component.

According to a third aspect, there are provided various uses of ligninthat has been treated by hydrothermal carbonization to improve theperformance of a pneumatic tyre.

According to a fourth aspect, there are provided various uses of a curedrubber based component comprising lignin that has been treated byhydrothermal carbonization to improve the performance of a pneumatictyre.

The invention is further presented in the detailed description of theinvention and in the independent and dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates, by way of an example, a pneumatic tyre for avehicle.

FIG. 2 illustrates, by way of an example, different types of functionalgroups of HTC lignin, which may be available for chemical reactions.

FIG. 3 illustrates, by way of an example, the concept of using anorganic molecule as a coupling agent for coupling HTC lignin and rubbertogether.

FIG. 4 illustrates, by way of an example, a nucleophilic substitutionreaction wherein a silane based coupling agent such as TESPT in used tocouple HTC lignin and rubber together.

FIG. 5 illustrates, by way of an example, the concept of using amethylene donor compound, such as hexa(methoxymethyl)melamine, forlinking together multiple separate HTC lignin particles.

FIG. 6 illustrates, by way of an example, the concept of using a phenolgroup of the HTC lignin with a methylene donor compound in order to forma cross-linked structure in a rubber based component of a pneumatictyre.

FIG. 7 represents, by way of examples, the results of aPyrolysis-Fourier transform infrared spectroscopy (pyro-FTIR) scan overa wavenumber range of ca. 850-1950 cm⁻¹ of pneumatic tyre samples.

FIG. 8 represents, by way of examples, the results of aPyrolysis-Fourier transform infrared spectroscopy (pyro-FTIR) scan overmid-infrared range of pneumatic tyre samples.

FIG. 9 represents, by way of an example, a GC chromatogram of apyrolysed sample comprising HTC lignin, displaying a spectral peakhaving a retention time around 13.5 minutes.

FIG. 10 represents, by way of an example, a GC chromatogram of apyrolysed sample comprising lignin, displaying a significantly smallerspectral peak having a retention time around 13.5 minutes.

FIG. 11 represents, by way of an example, a GC chromatogram of apyrolysed sample comprising carbon black, which does not display aspectral peak with a retention time around 13.5 minutes.

FIGS. 12 and 13 together represent, by way of an example, massspectrometry correlation data, proving that the spectral peak having aretention time around 13.5 minutes corresponds to 2-methoxyphenol.

FIGS. 14 to 16 each represents, by way of an example, athermogravimetric curve and a differential thermogravimetric curve,measured from a cured rubber based component as a function of time.

FIG. 17 represents, by way of an example, a thermogravimetric curve anda differential thermogravimetric curve, measured from a sample of HTClignin as a function of time.

FIG. 18 represents, by way of an example, a comparison of tangent deltavalues of cured rubber based components.

FIG. 19 represents, by way of an example, another comparison of tangentdelta values of cured rubber based components.

FIG. 20 represents, by way of an example, a comparison of modulus 300%values of cured rubber based components.

DETAILED DESCRIPTION

A Pneumatic Tyre

A pneumatic tyre in this context refers to a radial tyre used on a motordriven vehicle. Typical examples of pneumatic tyres are passenger car,SUV-, VAN-, bus and/or truck tyres. Pneumatic tyres, referred to asheavy tyres, may also be used in mining, harbour and forestryapplications.

A method for manufacturing a pneumatic tyre for a vehicle typicallycomprises manufacturing a preform of a pneumatic tyre, which is thencured. The manufacturing of a preform of a pneumatic tyre may comprisereceiving a rubber based component and arranging the rubber basedcomponent onto a building drum to form a tubular preform. When thetubular preform is expanded, a preform of a pneumatic tyre is obtained.Typically, metal components and textile components are arranged onto thepreform of a tyre.

Thus, a preform of a pneumatic tyre may comprise a metal component, atextile component and the rubber based component. The method furthertypically comprises curing of the preform of a pneumatic tyre. Curingmay be a vulcanization process, wherein the preform is heated in atemperature typically less than 200° C., such as in the range of 150 to200° C. During the curing reaction, sulphur containing compounds presentin the rubber based components undergo cross-linking reactions. Theformed cross-linked structure bonds the tyre components firmly together.The duration of the curing may vary. Passenger car tyres are typicallycured from few minutes up to half an hour, such as in the range of 5 to30 minutes. Heavy tyres may be cured for several hours.

Referring to FIG. 1. FIG. 1 is a sectional view of a pneumatic tyre TYR1up to a centerline Ax1. The centerline Ax1 divides the section width ofthe tyre TYR1 into two halves of equal width. The directions SX and SZdenote orthogonal directions. SX is a direction parallel to the sectionwidth and perpendicular to the plane of rotation of the tyre TYR1. SZ isa direction parallel to the centerline Ax1.

A pneumatic tyre TYR1 for a vehicle is typically manufactured ofmultiple components 1-15 and comprises a variety of materials, such asmetal, textile and multiple types of rubber based components. Ingeneral, a pneumatic tyre TYR1 may comprise one or more layers ofreinforcing textile, such as polyester or nylon for radial ply 8, aswell as nylon belts 4, 5. The pneumatic tyre TYR1 may comprise one ormore metal components for reinforcement purposes, such as resilientsteel belts 6, 7 and bead wire 9.

The metal component and the textile component are bonded to the tyreelastically by means of one or more rubber based components, when thetyre is cured. Due to the high complexity of a pneumatic tyre anddifferent materials used, the composition of each rubber based componentused at various locations in the tyre may have a significant effect onthe performance of the tyre. Each rubber based component used in a tyremay be arranged to provide a specific characteristic on the tyre. Therubber based components of a pneumatic tyre TYR1 may be divided intotread area components and non-tread area components.

The exterior of the tyre is called a tyre carcass, referring to a thickprofile surrounding the tyre. The tread area components in the tyrecarcass provide an interface between the tyre and the road. The treadarea components are thus components designed to be in contact with theroad. The area of the tyre that is designed to contact the road surfacemay also be denoted as the crown. The tread area components areconfigured to comprise wear resistance and traction. Hard tread areacomponents may provide less wear and reduce the rolling resistance ofthe tyre. Soft tread area components may provide better traction. Therubber based components of the tread area may comprise components suchas tread 1, tread base 2, undertread 3 and shoulder 15. A tread patternrefers to a tread surface configured to comprise surface deviation, suchas ribs, blocks, grooves and/or sipes, which may have an effect onnoise, handling, traction or wear of the tyre TYR1. The tread 1 maycomprise additional structural elements, such as metal studs. Theshoulder 15 refers to the area on both sides of the tread area, whichextends from the tread and ends at tread skirt. Tread skirt defines theintersection of tread area and sidewall area. The shoulder 15 maysometimes be referred to as shoulder wedge or tread wing.

The non-tread area components refer to component on the sidewall andbead areas of the tyre TYR1. The sidewall area components of a pneumatictyre TYR1 refers to components between the tread and the bead areas andcomprise, for example, sidewall 12. The sidewall is typically configuredto withstand flexing and provide protection for the ply 8. The bead areacomponents of a pneumatic tyre TYR1 may comprise, for example, clinch13, apex 10 and bead base 14. The clinch 13 and apex 10 may overlap bothon the sidewall and bead areas, and thus belong to both sidewall andbead area components. Apex 10 is configured to fill in the bead area andlower sidewall area. Apex 10 has the effect of providing a smoothertransition from the stiff bead area to the more flexible sidewall area.Clinch 13 is configured to be a reinforcing component between bead andlower sidewall. Clinch 13 acts as a stabilizing component. Clinch 13 hasthe effect of resisting rim chafing. Clinch 13 provides a smoothertransition from the stiff bead area to the more flexible sidewall area.Clinch 13 enables a proper seating of the bead base 14 to a rim flange,thereby enabling a tight sealing of the tyre with the rim flange. Thebead base 14, extending from bead toe to bead heel, is configured to actas a seal when in contact with the rim flange, such that the spacebetween innerliner 11 and the rim can be filled with compressed air.Innerliner 11 refers to a layer or layers of rubber or rubber basedcomponents. The innerliner 11 comprises a rubber composition configuredto resist air diffusion. When the space between the rim and thepneumatic tyre is inflated with high-pressure air, the innerlinercomponent reduces the air permeability of the tyre.

As described above with reference to FIG. 1, each tyre componentcomprising a rubber compound may be designed for a different purpose.Each component may therefore comprise a rubber compound designed toprovide dedicated performance characteristics for the tyre.

The tyre construction and materials together define the performancecharacteristics of the tyre, once fabricated and cured. The rubbercomposition used in different parts of a tyre may be varied. Theconsistency may also vary depending of the tyre type. The consistency ofa rubber based component of a summer tyre may be different thanconsistency of a rubber based component of a winter tyre. Theconsistency of a rubber based component between a studded tyre and anall season tyre may vary.

Carbon Black

Carbon black is typically used to provide tensile strength and wearresistance to a pneumatic tyre. Carbon black may be obtained by means ofincomplete combustion of fossile carbon source, such as heavy petroleumproducts. The most common method of manufacturing carbon black iscombustion of fossile oil or gas with oxygen inside a furnace, such thatmicroscopic carbon particles are formed. In a furnace reactor, thereaction rate is typically controlled by quenching, which refers tospraying of steam or water into the carbon particles.

Conventional carbon black used in rubber components of a pneumatic tyreis mainly elemental carbon, wherein the size of an individual particleof carbon black is in the range of 10 to 500 nanometers. Depending ofthe furnace conditions and used fossile carbon source, individualparticles of carbon black may be physically adhered to others of similarsize, thereby forming a cluster of carbon black particles. The clusterof carbon black particles typically consists of spherical particlesagglomerated together. The particles are structures capable to absorbfluids and reinforce materials such as rubber. Fluid absorbancy istypically referred to as oil absorbancy, and is a measure of dibutylphthalate absorption of the carbon black (ml/100 g). The reinforcingeffect of carbon black is principally due to morphologicalcharacteristics of the particles, enabling physical interactions in therubber based compound of a pneumatic tyre. In addition to elementalcarbon, carbon black can contain very small quantities of otherelements.

Carbon black can be graded e.g. based on ASTM D1765-14, which is usedfor classification of rubber-grade carbon blacks. The standard uses afour-character nomenclature system, wherein the first characterindicates the influence on the rate of cure and the second character,denoting the group number, gives information on the specific surfacearea of the carbon black. The last two characters are assignedarbitrarily. For example, N330 indicates a carbon black wherein thefirst character, letter N, stands for a carbon black producing a normalcure rate and the second character 3 stands for specific surface area,typically in the range of 70 to 99 m²/g. In general N100 to N300 gradecarbon black have a specific surface area which is larger than thespecific surface area of N500 to N900 grade carbon black. Typically,N500 to N900 grade carbon black comprise a specific surface area lessthan 70 m²/g. The determination of specific surface area can be doneaccording to standard ASTM D6556-10. Carbon black suitable for use inpneumatic tyres typically has a specific surface area of equal to orless than 150 m²/g. The group number further correlates with the averageparticle size. In general, the lower the surface area of carbon blackis, the lower is the cost and subsequently the poorer the reinforcementpotential of the material.

While e.g. precipitated or fumed silica has been used as a substitutefor carbon black as reinforcing material in rubber compositions fortyres, such raw materials have thus far been highly expensive comparedto carbon black.

Lignin as a Source of Functional and Renewable Material for PneumaticTyre

Lignin that has been treated by hydrothermal carbonization, denoted asHTC lignin, provides a new means for improving tyre performance. HTClignin may be manufactured from lignin containing material.

Lignin denotes a class of highly polymerized and branched, heterogeneousmacromolecules present in vascular plants. Lignin provides rigidity andstrength to cell walls of vascular plants. Plant lignin may be dividedinto three general classes comprising softwood (gymnosperm) lignin,hardwood (angiosperm) lignin and annual plant (graminaceous) lignin. Ingeneral, at least 15 wt. % of the dry weight of softwood or hardwood islignin. In different tree species the wood lignin content can vary,typically in the range of 15 wt. % to 40 wt. %. Spruce and pine areparticular examples of softwood sources having a high content of lignin.Wood based lignin is available as a by-product of the pulp and paperindustry. Lignin that has been treated by hydrothermal carbonization maytherefore comprise lignin of wooden origin, in particular lignin ofsoftwood origin. HTC lignin may further be manufactured inbiorefineries.

Lignin in native form has very high molecular weight. The molecularstructure of lignin comprises phenylpropane (C₉) units, which areconnected to each other, typically via carbon-carbon (C—C) and/or ether(C—O—C) linkages. The molecular structure of lignin thus compriseslignin precursor units, denoted as monolignols. When connected to eachother, the monolignols form the biopolymer referred to as lignin. Thelignin precursor units comprise different types of monolignols, such asconiferyl alcohol, sinapyl alcohol and/or p-coumaryl alcohol. Guaiacyllignin refers to lignin comprising principally precursor units ofconiferyl alcohol. Syringyl refers to lignin comprising precursor unitof both coniferyl alcohol and sinapyl alcohol. In general, softwoodlignin comprises principally guaiacyl. Hardwood lignin typicallycomprises both guaiacyl and syringyl.

A Method for Hydrothermal Carbonization of Lignin

As described above, a hydrothermal carbonization treatment may be usedto break the macromolecular structure of lignin. Lignin that has beentreated by hydrothermal carbonization, denoted as HTC lignin, provides arenewable source of material, which may be used in a rubber compound ofa pneumatic tyre.

Hydrothermal carbonization of lignin refers to a method comprisingreceiving lignin containing material and treating the lignin containingmaterial in an aqueous suspension at elevated pressure and temperature.A hydrothermal carbonization of lignin thus comprises a stage, whereinlignin containing material is subjected to partial decomposition bymeans of heat in a liquid environment. A hydrothermal carbonization oflignin refers to a thermochemical process configured to convert lignincontaining medium into a lignin derivative of substantially uniformquality, wherein the lignin derivative contains functional groups. Themethod may comprise selecting thermochemical conversion processconditions for treating the lignin containing material, such that ligninderivative with distinguishable characteristics may be obtained.Characteristics typical to lignin derivate may be determined from arubber based component of a pneumatic tyre.

The method for hydrothermal carbonization of lignin further comprises atleast partial refining of the lignin containing material. Typically, thelignin may be at least partially charred. During the hydrothermalcarbonization treatment, the lignin is surrounded by water. The extentof decomposition of lignin in the hydrothermal carbonization may beadjusted, for example by means of process temperature, pressure, and/orby selecting the pH of the water suspension. The method for hydrothermalcarbonization of lignin may comprise selecting the reaction conditionsof the hydrothermal carbonization, thereby forming HTC lignin withdefined properties. The method may comprise selecting the surroundingmedium parameters, such as pH and pressure, the maximum temperatureand/or the residence time of the input material, such that HTC ligninhaving different characteristics is obtained.

Hydrothermal carbonization of lignin may be carried out in a reactor.The reactor may be, for example, a batch reactor suitable for chemicalreactions. Batch process, such as a single batch process, is an exampleof a convenient way to control the process conditions of a hydrothermalcarbonization treatment. The method for hydrothermal carbonization oflignin may comprise controlling the internal pressure of the reactorsuch that the water inside the reactor is maintained in a liquid stateduring the hydrothermal carbonization. The internal pressure of thereactor during hydrothermal carbonization reaction may be in the rangeof 10 to 40 bar, preferably equal to or higher than 15 bar. The methodfor hydrothermal carbonization of lignin may comprise controlling thetemperature of the aqueous suspension containing lignin, such that thelignin starts to break down to smaller fragments. The temperature of ahydrothermal carbonization reaction may be higher than 150° C.Typically, the temperature of a hydrothermal carbonization reaction isless 300° C., such as in the range of 150 to 250° C. The temperature ofa hydrothermal carbonization reaction refers to the temperature of theaqueous suspension inside the reactor vessel during the hydrothermalcarbonization reaction.

The method for hydrothermal carbonization of lignin may comprisecontrolling the pH of the aqueous suspension containing lignin. Ligninis highly soluble in alkaline conditions. The pH of the suspensioncontaining lignin in the hydrothermal carbonization treatment has aneffect on the particle size of the formed lignin derivative. The methodfor hydrothermal carbonization of lignin may comprise adjusting the pHof the suspension containing lignin to a pH value above 7, preferablyabove pH value 8. The pH of the aqueous suspension containing lignin maybe adjusted before a hydrothermal carbonization treatment. In alkalinesuspension, typically in a pH equal to or higher than 10, thepolymerization of lignin may be suppressed. The particle size of HTClignin is dependent of the pH chosen for the hydrothermal carbonizationtreatment. The method for hydrothermal carbonization of lignin maycomprise reducing the hydrogen ion (H⁺) concentration of an aqueoussuspension containing lignin prior to hydrothermal carbonization,thereby reducing the particle size of the formed HTC lignin. The methodfor hydrothermal carbonization of lignin may comprise increasing thehydrogen ion (H⁺) concentration of an aqueous suspension containinglignin prior to hydrothermal carbonization, thereby increasing theparticle size of the formed HTC lignin. The particle size of HTC ligninrefers to the average particle size after the hydrothermal carbonizationtreatment. The average particle size of HTC lignin can be determined bythe same means as the average particle size of carbon black, asdescribed above. The specific surface area of HTC lignin can bedetermined according to standard ASTM D6556-10, as described above.

Characteristics of HTC Lignin Suitable for Pneumatic Tyre

A HTC lignin particle comprises a polymeric structure, which may bearranged to provide a filler material, which is more flexible thansilica or carbon black. Phenol groups and aromatic alcohols in themolecular chain may be arranged to provide rigidity into the structureof a rubber based component. Due to the polymeric structure of the HTClignin particle, the link, referring to the distance, between the fillermaterial and rubber may be extended. The linker thus becomes longer thanwith other conventional filler materials, such as silica. A rubber basedcomponent comprising HTC lignin therefore may provide higher tensilestrength, higher tear resistance and/or improve abrasion resistance in apositive manner.

In general, HTC lignin suitable for a rubber based component of apneumatic tyre may have a specific surface area of less than 150 m²/g,when determined according to ASTM D6556-10, the specific surface areareferring to the total surface area based on multipoint nitrogenadsorption. Typically, HTC lignin suitable for a rubber based componentof a pneumatic tyre has a specific surface area of less than 100 m²/g,such as in the range of 10 to 100 m²/g,

HTC lignin suitable for a rubber based component of a pneumatic tyre mayhave and oil absorption number of less than 130 ml/100 g, when measuredaccording to ASTM D2414-09. Typically, HTC lignin suitable for a rubberbased component of a pneumatic tyre has an oil absorption number of lessthan 120 ml/100 g, such as in the range of 60-100 ml/100 g. The oilabsorption number correlates with the amount of fluid the material canabsorb internally, and is proportional to the reinforcing capability ofthe material.

Elementary composition of HTC lignin typically comprises high amounts ofelemental carbon. HTC lignin may contain elemental carbon 40 wt. % ormore, such as in the range of 40 to 65 wt. %, or even higher. HTC ligninmay contain oxygen less than 30 wt. %, typically in the range of 15 and20 wt. %. HTC lignin may contain nitrogen less than 20 wt. %, typicallyin the range of 3 to 6 wt. %. HTC lignin may optionally contain minoramounts of sodium, such as equal to or less than 2 wt. %. HTC lignin mayoptionally contain minor amounts of sulphur, such as equal to or lessthan 3%. The elementary composition of HTC lignin, including the carboncontent, may be determined by analytical methods for biochar analysisaccording to the European Biochar certificate (version 4.1, 4 Mar.2014).

HTC Lignin Functional Groups

The chemical structure of HTC lignin may comprise different types offunctional groups. The chemical structure of HTC lignin typicallycomprises functional groups such as hydroxyl, carboxyl, methoxy and/orphenolic hydroxyl groups. A method to detect functional groups presentin HTC lignin may comprise analyzing the HTC lignin by an analyticalmethod, such as Fourier transform infrared spectroscopy (FTIR), nuclearmagnetic resonance of phosphorus (³¹P-NMR) or Heteronuclear SingleQuantum Correlation (HSQC) spectroscopy. Such analytical method istypically performed with an analytical instrument suitable for suchmethod and according to the manufacturer's instructions.

HTC lignin comprises a molecular structure, which has capability toreinforce a rubber based component both by physical interaction as wellas chemical bonding. The molecular structure of HTC lignin is much morecomplex than the structure of conventional fillers, such as carbonblack, for example. HTC lignin contains less aliphatic hydroxyl groupsthan non-processed lignin. Non-processed lignin refers to lignin innative form.

The method for hydrothermal carbonization of lignin comprises enrichmentof the of the carbon content of the lignin. Hydrothermal carbonizationof lignin thus involves reactions, which are configured to increase thecarbon content of the input material. The enrichment of the carboncontent of the lignin treated by hydrothermal carbonization may occur bymeans such as dehydration and decarboxylation, which result in formationof carbon dioxide (CO₂), oxygen and hydrogen cleavage. At lowertemperatures, the dehydration dominates, at higher temperatures thedecarboxylation dominates. At higher temperature more carbon is thuscleaved off. At higher temperatures both the dehydration and thedecarboxylation reactions proceed more rapidly. Hence, the method forhydrothermal carbonization of lignin may comprise increasing thetemperature of the reaction temperature, thereby reducing the residencetime.

Hydrothermal carbonization treatment of lignin has the effect ofpreserving the surface active functional groups of the input lignincontaining material, to at least some extent. HTC lignin thus comprisesfunctional groups which are capable of bonding with other compounds in achemical reaction. A hydrothermal carbonization of lignin providesmaterial having relatively high amount of surface active functionalgroups. By relatively high amount of surface active functional groups itis meant, that after the hydrothermal carbonization of lignin the amountof functional groups, such as aliphatic hydroxyl groups, may be lessthan the amount of functional groups before the hydrothermalcarbonization of lignin. The amount of functional groups is however,considerably higher than in carbon black, for example.

The method for hydrothermal carbonization of lignin comprises producingdegraded fragments of lignin, denoted as lignin derivatives. Lignin thathas been treated by hydrothermal carbonization process thus compriseslignin derivatives. An example of a lignin derivative is2-methoxyphenol, also referred to as o-guaiacol. By controlling theconditions and duration of the hydrothermal carbonization treatment, thecharacteristics of the produced lignin derivatives may be affected. Forexample, the lignin derivatives may be arranged to link to each other.Such linking may occur, for example, via elimination and/or condensationreactions.

Chemical Bonding of a Rubber Compound Comprising HTC Liqnin

The functional groups in HTC lignin are capable of forming chemicalbonds. A rubber based component of a pneumatic tyre which comprises HTClignin may form chemical bonds. HTC lignin may react with rubbercompounds by different types of reaction mechanisms.

With reference to FIGS. 2 and 3, HTC lignin ORG1 may comprise a varietyof different types of functional groups R^(x). HTC lignin ORG1 maycomprise a number of functional group R^(x). Each functional group R^(x)may independently be, for example,

-   -   a hydroxyl group (—OH),    -   a carboxyl group (—COOH),    -   a benzylic hydroxyl group (—C₇H₈O) or    -   a phenolic hydroxyl group (—C₆H₅OH).

The functional group R^(x) is a surface active group, which is capableof reacting with a functional group R¹ of a coupling agent. A couplingagent refers to an organic molecule AGT1 comprising a first functionalgroup R¹ capable to form a covalent bond with a functional group R^(x)of HTC lignin ORG1 and a second functional group R² capable to form acovalent bond with a rubber compound RUB1. The first functional group R¹and the second functional group R² of the organic molecule AGT1 may beseparated by an organic spacer SPC1.

The first functional group R¹ of the organic molecule AGT1 mayindependently be, for example, an group, an epoxy group, a beta-ketoester group, a phenol hydroxyl group or a silanol group. The secondfunctional group R² of the organic molecule AGT1 may independently be,for example, a vinyl group (—CH═CH₂), a thiol group (—SH) or a sulphurchain (—S—(S)_(n)—S—), wherein n represents the number of sulphur atoms.The number of sulphur atoms is typically equal to or less than 20, suchas between 1 and 20. The organic spacer SPC1 may be a hydrocarbon chainof variable length. The spacer SPC1 may have a linear, branched orcyclic structure. The spacer SPC1 may contain saturated and/orunsaturated bonds. The spacer SPC1 may contain heteroatoms, such asnitrogen, oxygen or sulphur.

HTC lignin may be arranged to comprise one or more distinct structuralfeatures, which enable a chemical reaction mechanism to take place. SuchHTC lignin is suitable for chemical interaction in a rubber basedcomponent of a pneumatic tyre. HTC lignin may be arranged to comprisecarbolic acid functionality. Carbolic acids in this context refer tophenols.

HTC lignin is a macromolecule, which may be arranged to comprisephenolic rings, wherein at least some of the phenolic rings contain afree ortho-position on the phenolic ring. The free ortho-position on thephenolic ring enables electrophilic aromatic substitution reactions. Anexample of an electrophilic aromatic substitution reaction is a reactionof HTC lignin with a methylene donor, such as hexamethylenetetramine orhexa(methoxymethyl)melamine.

An example of a compound having a free ortho-position on the phenolicring is 2-methoxyphenol. A rubber based component of a pneumatic tyremay comprise HTC lignin and 2-methoxyphenol. A rubber based component ofa pneumatic tyre may comprise HTC lignin, wherein the HTC ligninmacromolecule is configured to have aromatic reactivity by means of freephenolic hydroxyl groups. HTC lignin may comprise structure, wherein2-methoxyphenol is covalently bound to the macromolecular structure ofthe HTC lignin. Such HTC lignin is in this context referred to as HTClignin having 2-methoxyphenolic functionality. 2-methoxyphenol may bebound to HTC lignin such that the free phenolic hydroxyl group of the2-methoxyphenol is in a para-position. A rubber based component may inaddition be arranged to contain HTC lignin and 2-methoxyphenol, suchthat the 2-methoxyphenol is present as a separate substance, such asaromatic oil. Aromatic oils are typically volatile and may generate adistinct odour when evaporating. The presence of 2-methoxyphenolicfunctionality in a rubber based component may be detected, both whenpresent as a covalently bound structure or as a volatile substance. Thepresence of 2-methoxyphenol may be detected, for example, from apyrolysis product of a cured rubber based component of a pneumatic tyre.HTC lignin containing 2-methoxyphenol and/or 2-methoxyphenolicfunctionality has been observed to be particularly suitable for use in arubber based component of a pneumatic tyre.

HTC lignin may be arranged to comprise phenolic rings, wherein at leastsome of the phenolic rings contain a phenoxide ion. A phenoxide ion ishighly reactive towards an electrophilic attack. A phenolic ring withfree ortho-position may also react with β-ketoesters via Pechmanncondensation to form a coumarin type structure.

HTC lignin may be arranged to comprise hydroxyl groups. HTC lignincomprising one or more hydroxyl groups may be arranged to react viadifferent chemical reaction mechanisms. HTC lignin may comprise hydroxylgroups, which are aliphatic, phenolic or a combination of both. Thealiphatic hydroxyl groups may be primary and/or secondary hydroxylgroups. HTC lignin comprising hydroxyl groups may be arranged toparticipate in different types of chemical reactions. Hydroxyl groups ofHTC lignin may participate in a tosyl-activated reaction, in an openingreaction with an epoxide, in an esterification with carboxylic acid andanhydride or in a silylation reaction with a silane. For example, ahydroxyl group of the HTC lignin may react with a coupling agentcomprising an alkyl tosylate via nucleophilic substitution, referred toas S_(N)2 mechanism. Alternatively, a hydroxyl group of the HTC ligninmay react with a coupling agent containing an epoxide ring, therebycausing the epoxide ring to open and enabling a covalent bond to formbetween the HTC lignin and the coupling agent. HTC lignin may react witha coupling agent containing an ester, wherein the carbonyl carbon of theester may be attacked by an alkoxide ion or phenolic hydroxyl groupacting as a nucleophile via an addition reaction, followed byelimination of yet another alkoxide ion or alcohol, thereby forming acovalent bond between the HTC lignin and the coupling agent. HTC ligninmay react with a coupling agent containing beta-keto ester, such that anesterification reaction takes place, followed by ring closure andlactone formation, thereby forming a covalent bond between the HTClignin and the coupling agent. In each example above, the coupling agentmay in addition to the first functional group comprise a secondfunctional group capable to form a covalent bond with a rubber compound,such that the HTC lignin and rubber may be cross-linked together bymeans of a coupling agent. The coupling agent may be used as a means forcoupling HTC lignin and rubber compound, thereby modifying theviscoelastic properties of a rubber based component.

Referring to FIG. 4, HTC lignin ORG1 may react with the coupling agentvia nucleophilic substitution reaction. An example of a nucleophilicsubstitution is the reaction betweenbis-[3-(triethoxysilyl)-propyl]-tetrasulfide and HTC lignin ORG1.Bis-[3-(triethoxysilyl)-propyl]-tetrasulfide, hereafter referred to asTESTP, is an example of a silane based coupling agent. The silanolgroups of TESPT, i.e. triethoxysilyl groups, are capable of reactingwith HTC lignin containing a hydroxyl group. The structure of HTC ligninmay contain a carboxyl group and/or a phenyl group, which both contain ahydroxyl group. Both the carboxyl group and the phenyl group areindependently suitable for reaction with a silanol group of a couplingagent. The silanol group of TESPT may further react with synthetic ornatural rubber, such a styrene-butadiene rubber. When acting as acoupling agent, TESPT may form a first chemical bond with HTC lignin anda second chemical bond with rubber, thereby forming a structure in therubber based component, wherein the HTC lignin and rubber have beencross-linked together by means of a coupling agent. TESPT therefore mayact as an interfacial coupling layer between HTC lignin and rubber inthe rubber based component.

HTC lignin may be used together with a methylene donor compound in arubber based component of a pneumatic tyre to provide a componentcomprising high modulus, stiffness and reinforcement. A methylene donorcompound is typically capable of generating formaldehyde when subjectedto heating. Traditionally, a rubber based component comprising highmodulus, stiffness and reinforcement has been obtained by mixingmethylene donor compound and phenolic resin. The phenolic resins reactwith the methylene donor compound during vulcanization process, therebycreating a reinforcing network structure to the cured rubber basedcomponent. At the same time the brittleness and hardness of the curedrubber based component is highly increased and elasticity is highlydecreased. As an alternative for high stiffness, the rubber basedcomponent may comprise high amounts of reinforcing filler and a curingchemical, such as sulphur or sulphur donor. However, the reinforcingeffect is not as high as with phenolic resins with methylene donorcompound. HTC lignin may interact with a methylene donor compound,thereby providing a cross-linked polymer structure which has thecapability to reinforce a rubber based component of a pneumatic tyre.The combination acts as a reinforcing agent capable of forming networkstructures. A rubber based component comprising HTC lignin isparticularly suitable with a methylene donor compound, when the rubberbased component comprises HTC lignin in amounts less than 10% by weightof the rubber based component, such as in the range of 0.5 to 9.5 wt. %,preferably in the range of 2 to 9 wt. %, of the total weight of therubber based component. A rubber based component comprising HTC ligninand a methylene donor compound is preferably a non-tread area component,such as a sidewall area component or a bead area component of apneumatic tyre. Sidewall in particular needs to withstand flexing.

A methylene donor compound suitable for use with HTC lignin is acompound, which is capable to form a network structure with lignin thathas been treated by hydrothermal carbonization. An example of amethylene donor compound is a polyamine based hardening resin. Apolyamine based hardening resin refers to a compound that may with HTClignin undergo a self-condensation reaction. Such compound is underacidic conditions capable to form a network structure with lignin thathas been treated by hydrothermal carbonization. By “under acidicconditions” it is meant, that a methylene donor compound suitable foruse with HTC lignin has an affinity to form a network structure with HTClignin, which can be demonstrated under controlled conditions e.g. in alaboratory experiment. HTC lignin comprises one or more functionalgroups capable of forming chemical bonds, which may be arranged to forma network structure with such methylene donor compound. Examples of apolyamine based hardening resin are compounds such ashexamethylenetetramine and hexa(methoxymethyl)melamine, typicallyabbreviated as HMT and HMMM, respectively. The combination of HTC ligninand polyamine based hardening resin may be used to improve the abrasionresistance and initial tear strength of a rubber based component of apneumatic tyre.

The amount of methylene donor compound to be used together with the HTClignin may be selected depending of the chemical composition of themethylene donor compound. Typically, the concentration ratio of phenolgroups (with free ortho position) of the HTC lignin and amino groups ofthe methylene donor in the reaction may be stoichiometric. However, theamount of the methylene donor may be lower or higher than the amount ofphenol groups of the HTC lignin, if desired. In particular, when themethylene donor amount is lower, the brittleness of the formedreinforcing, cross-linked polymer structure is not too high. The ratioof the methylene donor compound to the HTC lignin may be in the range1:20 to 10:1, preferably in the range of 1:10 to 3:1, determined as aweight ratio. Reaction with the HTC lignin and the methylene donorincreases the stiffness and strength of the rubber based component anddecreases the heat generation without significantly affecting the breakstrain and elasticity of the rubber based component, when compared to arubber based component having a phenolic resin based network structure.

Referring to FIG. 5, the organic molecule may be a methylene donorcompound MET1, such as hexa(methoxymethyl)melamine, linking togethermultiple separate HTC lignin molecules, such as a first HTC ligninmolecule ORG1 and a second HTC lignin molecule ORG11, thereby enabling across-linking structure to be formed in a rubber based component.

Referring to FIG. 6, a phenol group of the HTC lignin may react with amethylene donor compound, in this case hexamethylenetetramine. Thereaction may take place in an acid catalyzed reaction. A methine groupformed in the equilibrium reaction under acidic conditions reacts intothe ortho-position in the phenol ring of the HTC lignin. In a subsequentreaction, a heterocyclic ring structure bearing an iminium ion isformed. The formed iminium ion reacts further via an electrophilicaromatic substitution with a phenol ring of another HTC lignin molecule.Hexamethylenetetramine thus links separate HTC lignin moleculestogether, thereby enabling a cross-linking structure to be formed in arubber based component. HTC lignin may be configured to react with amethylene donor compound such as hexamethylenetetramine in a similarmanner as phenol-formaldehyde resins, generally referred to as phenolicresins or novolacs. HTC lignin may thus be used to replace phenolicresins in rubber based components of a pneumatic tyre.

HTC Lignin Amounts in a Rubber Based Component of a Pneumatic Tyre

The characteristics of a rubber based component of a tyre may be chosen,for example, by selecting the HTC lignin content, particle morphology,particle size, and/or average particle size distribution used for saidrubber based component. For the purpose of replacing carbon black, arubber based component of a pneumatic tyre may typically comprise HTClignin in an amount of equal to or less than 75 wt. %, such as in therange of 1 to 70 wt. %, of the total weight of the rubber basedcomponent.

For the purpose of replacing a defined grade of carbon black, having adefined reinforcing effect, the HTC lignin to be added into a rubbercomposition may be selected such that the specific surface area of theHTC lignin produces a reinforcing effect corresponding to thereinforcing effect of carbon black grade being replaced. A method formanufacturing a pneumatic tyre for a vehicle may comprise receiving arubber based component comprising HTC lignin. The method may comprisereceiving a rubber based component, wherein HTC lignin has been mixedwith rubber after polymer addition. Other raw materials of the rubberbased component have preferably been added later, after the HTC ligninhas been mixed with the rubber. Preferably, HTC lignin has been mixedwith the rubber at a temperature in the range of 130° C. to 170° C.Temperatures lower than 130° C. may not be high enough to achievechemical bonding of HTC lignin with coupling agent. In temperaturesabove 170° C. polymer compounds typically added into the rubbercomposition of a pneumatic tyre may break down, which may lead toreduced characteristics of the rubber based component comprising HTClignin.

The characteristics of a rubber composition in a tyre component may befurther affected by a combination of HTC lignin and a coupling agent.When the rubber based component further comprises a silane basedcoupling agent, HTC lignin has preferably been mixed with the rubber ata temperature in the range of 130° C. to 160° C. When the coupling agentis bis-[3-(triethoxysilyl)-propyl]-tetrasulfide (TESPT), HTC lignin haspreferably been mixed with the rubber at a temperature in the range of130° C. to 160° C. Temperatures higher than 160° C. can causepolysulfide chains of TESPT to break down, thereby causingpre-vulcanization.

A cured rubber based component of a pneumatic tyre may comprise HTClignin in an amount of equal to or less than 75 wt. %, preferably in therange of 1 to 70 wt. %. Cured rubber based component comprising HTClignin in amounts equal to or more than 10 wt. % are contemplated to beparticularly beneficial for reducing rolling resistance of a pneumatictyre, in particular when the rubber based component is located in anon-tread area of the tyre, such as in the sidewall or bead areacomponents. Preferably, the cured rubber based component may compriseHTC lignin equal to or more than 10 wt. %, such as in the range of 20 to60 wt. %, of the total weight of the cured rubber based component, whenused for reducing rolling resistance of a pneumatic tyre.

When the rubber based component is located in a tread or non-tread areaof the tyre in combination with a coupling agent, the rubber basedcomponent may comprise HTC lignin in the same amounts as disclosedabove. The HTC lignin in the rubber based component may be used toreduce the amount of silica. HTC lignin in the rubber based componentmay replace silica in whole. HTC lignin comprises novel propertiescompared to conventional carbon black or silica, as the amount ofphysical and chemical interaction of the filler with the rubbercompounds may be adjusted. The amount of physical and chemicalinteraction of the filler with the rubber compounds may be adjusted, forexample, by selecting the a coupling agent and the amount of couplingagent.

A Method for Detecting Functional Groups of HTC Lignin from a RubberBased Component of a Pneumatic Tyre

Referring to FIG. 7. Functional groups of lignin and lignin derivativesmay be detected from a cured rubber based component by analyticalmethods. FIG. 7 is a diagram representing results of a Pyrolysis-Fouriertransform infrared spectroscopy (pyro-FTIR) analysis, performed to threetyre samples CMP1, CMP2 and CMP3 according to standard ASTM D3677-10.The FTIR instrument was Nicolet iS10 (ThermoFisher Scientific) withdiamond ATR unit, used according to manufacturer's instructions.

Each sample CMP1, CMP2, CMP3 of cured rubber based component waspyrolysed at 600° C. At this temperature each sample was converted to apyrolysis product. Sample CMP1 was a cured rubber based componentcomprising 46 phr of lignin that had not been treated by hydrothermalcarbonization. Sample CMP2 was a cured rubber based component comprising46 phr of HTC lignin, referring to lignin that had been treated byhydrothermal carbonization. Sample CMP3 was a cured rubber basedcomponent comprising 46 phr of N660 grade carbon black. Sample CMP3 wasa reference sample, which did not contain lignin in any form.

FTIR analysis is a measure how well a sample absorbs infrared radiationat each wavelength. FTIR diagram represents a spectrum of the signalabsorbance at a selected wavelength range. The mid-infrared range,corresponding to wavenumbers approximately within the range of 4000 to400 cm⁻¹, may be used to study the fundamental vibrations and associatedrotational-vibrational structure. In FIG. 8, the vertical axisrepresents the signal absorbance measured in logarithmic units ofreflectance R (log [1/R]). The horizontal axis represents the wavenumber (cm⁻¹). FTIR allows qualitative analysis of the cured rubbercomponent, as different chemical bonds have specific vibrationalproperties at given wave numbers, which may be detected.

The results of FTIR analysis demonstrate that the sample CMP1 comprisesan infrared spectrophotometry absorption band in the range of 1259 to1269 cm⁻¹. The band comprises two peaks, the peak with higherabsorbance, denoted as peak maximum, positioned around 1269 cm⁻¹. Theabsorbance intensity level at peak maximum, positioned around 1269 cm⁻¹,was approximately 0.09, which intensity level clearly differs from thebaseline intensity level of the neighboring range. The results of FTIRanalysis further demonstrate that the sample CMP2 also comprises aninfrared spectrophotometry absorption band in the wavenumber range of1259 to 1269 cm⁻¹. The band also comprises two peaks, the peak withhigher absorbance, denoted as peak maximum, positioned around 1259 cm⁻¹.The absorbance intensity level at peak maximum, positioned around 1259cm⁻¹, was approximately 0.07, which intensity level clearly differs fromthe baseline intensity level of the neighboring range. Said wavenumberband in the range of 1259 to 1269 cm⁻¹ is characteristic to C—O bond ofphenolic groups and/or aromatic structures comprising hydroxyl-,carboxyl- and/or metoxy groups. Such groups are typical in lignin thathas been treated by hydrothermal carbonization. The sample CMP3 does notcomprise an infrared spectrophotometry absorption band in the range of1259 to 1269 cm⁻¹. The absorbance intensity level at the range of 1259to 1269 cm⁻¹ was approximately 0.04, which intensity level does notsignificantly differ from the baseline intensity level of theneighboring range. HTC lignin, when pyrolysed at 600° C. according tostandard ASTM D3677-10, thus comprises an infrared spectrophotometryabsorption peak maximum around 1259 cm⁻¹. Thus, FTIR absorption in thisrange may be used as specific indication means for detecting thepresence of lignin or lignin derivative in a cured rubber basedcomponent of a tyre.

The results of the FTIR analysis further demonstrate an absorbanceintensity level difference between the samples CMP1, CMP2 comprisinglignin or HTC lignin and the sample CMP3 not containing any ligninderivative. In a first wavenumber range RNG1 of 1200 to 1250 cm⁻¹,sample CMP1 has an absorbance intensity level AB1 close to 0.08 inlogarithmic absorbance units (log [1/R]), sample CMP2 has an absorbanceintensity level AB2 close to 0.06 in logarithmic absorbance units (log[1/R]) and sample CMP3 has an absorbance intensity level AB2 close to0.04 in logarithmic absorbance units (log [1/R]). This absorbanceintensity level difference is most likely related to asymmetricstretching vibrations of C—O—C linkages in ethers and esters of ligninderivatives, which may be present in the samples CMP1 and CMP2. Asimilar absorbance intensity level difference between the samples CMP1,CMP2 comprising lignin or HTC lignin and the sample CMP3 not containingany lignin derivative is demonstrated in a second wavenumber range RNG2around 1515 cm⁻¹. Thus, FTIR absorption intensity level in either thefirst or both of the first and second ranges RNG1, RNG2 may be used asspecific indication means for determining the presence of lignin orlignin derivative from a cured rubber based component of a tyre.

FIG. 8 is a diagram representing the Pyrolysis-Fourier transforminfrared spectroscopy (pyro-FTIR) analysis on mid-infrared range tosamples CMP1, CMP2 and CMP3 according to standard ASTM D3677-10, asdisclosed above. The results of the FTIR analysis demonstrate a furtherabsorbance intensity level difference between the samples CMP1, CMP2comprising lignin or HTC lignin and the sample CMP3 not containing anylignin derivative. In a third wavenumber range RNG3 of 3600 to 3100cm⁻¹, sample CMP3 has an absorbance intensity level, which is lower thanthe absorbance intensity level of either sample CMP1 comprising ligninor sample CMP2 comprising HTC lignin. This absorbance intensity leveldifference is most likely related to vibrations of hydroxyl groups oflignin derivatives, which may be present in the samples CMP1 and CMP2.

A Method for Detecting HTC Lignin from a Rubber Based Component of aPneumatic Tyre by Pyro-GC-MS Analysis

Referring to FIGS. 9, 10 and 11. The hydrothermal carbonizationtreatment produces lignin derivatives with distinguishablecharacteristics, which may be detected from a cured rubber component ofa pneumatic tyre. Thus, the presence of HTC lignin may be detected froma rubber based component of a pneumatic tyre by an analytical methodknown as pyrolysis-gas chromatography-mass spectrometry, abbreviated aspyro-GC-MS. Pyro-GC-MS is a chemical analysis method in which a sampleis pyrolysed, thereby producing a pyrolysis product of the cured rubbercomponent of a pneumatic tyre. When performing a pyrolysis-gaschromatography-mass spectrometry analysis on a cured rubber basedcomponent, such as vulcanized rubber product, the cured rubber basedcomponent is first treated by acetone. Acetone treatment, typicallyreferred to as acetone extraction, removes rubber resins, free sulfur,acetone-soluble plasticizers, processing aids, mineral oils or waxes,acetone-soluble antioxidants and organic accelerators or theirdecomposition products, and fatty acids. It also removes part ofbituminous substances, vulcanized oils, high molecular masshydrocarbons, and soaps. The portion extracted from the cured rubberbased component is generally called an acetone extract. An acetoneextract treatment suitable for a cured rubber based component isdescribed in sections 18 and 19 of the standard D297-93 (reapproved2006). A pyrolysis-gas chromatography-mass spectrometry analysis may beperformed on the remaining part of the cured rubber based component,after acetone extraction treatment. Pyrolysis refers to thermaldecomposition of material in an inert atmosphere or a vacuum. Thepyrolysis product comprises smaller molecules, which are furtherseparated by gas chromatography. In general, each separated smallermolecule of the pyrolysis product has a specific retention time,referring to the time from sample injection to sample elution in the gaschromatography column. Each separated smaller molecule having a specificretention time may be further identified using mass spectrometrydownstream of the gas chromatography column. In FIGS. 9, 10 and 11, thevertical axis represents the response of the GC detector unit to eachpeak in percentage units (%). The horizontal axis represents theretention time from sample injection in minutes. The minutes aredisplayed as discrete minutes with hundredth parts.

FIG. 9 represents a pyrolysis GC chromatogram of a first sample fromcured rubber based component of a pneumatic tyre comprising HTC ligninafter acetone extraction treatment, as described above. The sample was acured rubber based component comprising 46 phr of HTC lignin, referringto lignin that had been treated by hydrothermal carbonization, andcorresponded to the sample CMP2 of the FTIR analysis. The sample waspyrolysed at 550° C. according to standard ASTM D3452-06, therebyproducing material referred to as a pyrolysis product. The pyrolysisproduct was injected to a chromatographic column and eluted. Thepyrolysis product produced a gas chromatographic spectral peak with aretention time around 13.5 minutes. The response of the GC detector unitto was around 60%. This is indicated as the higher peak in the middle ofthe timeline in FIG. 9, corresponding to a retention time with a peakmaximum at a time point around 13 and half minutes.

FIG. 10 represents a pyrolysis GC chromatogram of a second sample fromcured rubber based component of a pneumatic tyre comprising lignin afteracetone extraction treatment, as described above. The sample was a curedrubber based component comprising 46 phr of lignin, referring to ligninthat had not been treated by hydrothermal carbonization, andcorresponded to the sample CMP1 of the FTIR analysis. The sample wasprepared as disclosed above and the pyrolysis product was injected to achromatographic column and eluted. The pyrolysis product produced a gaschromatographic spectral peak with a retention time around 13.5 minutes.This is indicated as the higher peak in the middle of the timeline inFIG. 10, corresponding to a retention time with a peak maximum at a timepoint around 13 and half minutes. The response of the GC detector unitto was around 20%. The ratio of the spectral peak height of the firstsample containing HTC lignin to the spectral peak height of the secondsample containing lignin that had not been treated by hydrothermalcarbonization was in the range of 3:1. The cured rubber based componentcomprising lignin thus produced a significantly lower response of the GCdetector unit. The difference is visually detectable, when comparing thespectral peak heights of FIGS. 9 and 10.

FIG. 11 represents a pyrolysis GC chromatogram of a third sample fromcured rubber based component of a pneumatic tyre after acetoneextraction treatment, as described above, which sample did not compriselignin. The sample was a cured rubber based component comprising 46 phrof N660 grade carbon black, and corresponded to the reference sampleCMP3 of the FTIR analysis. The sample was prepared as disclosed aboveand the pyrolysis product was injected to a chromatographic column andeluted. The pyrolysis product did not produce a gas chromatographicspectral peak with a retention time around 13.5 minutes. The GC detectorunit had an essentially flat baseline level below 10%.

The results demonstrate that gas chromatography may be used to detectthe presence of the HTC lignin from a pyrolysis product of a curedrubber based component of a pneumatic tyre. HTC lignin produces aneluted fragment with a retention time around 13.5 minutes. The elutedfragment is not present in cured rubber based component of a pneumatictyre comprising only carbon black.

Referring to FIGS. 12 and 13. The eluted fragment with a retention timearound 13.5 minutes from the sample containing HTC lignin was analyzedwith a mass spectrometer downstream of the gas chromatography. Thevertical axis represents the intensity (%). The horizontal axisrepresents the mass-to-charge (m/z). FIG. 12 represents the massspectrum of the eluted fragment with a retention time around 13.5minutes from a pyrolysis product of a cured rubber based component of apneumatic tyre comprising HTC lignin. FIG. 13 represents the massspectrum of 2-methoxyphenol. The mass spectrum of the eluted fragmentwith a retention time around 13.5 minutes from a pyrolysis product of acured rubber based component of a pneumatic tyre comprising HTC ligninmatches with the mass spectrum of 2-methoxyphenol.

As demonstrated above, the presence of HTC lignin which contains2-methoxyphenol may be determined from a rubber based component of apneumatic tyre by means pyro-GC-MS analysis.

Detection of HTC Lignin from a Rubber Based Component of a PneumaticTyre by Thermogravimetric Analysis

Presence of HTC lignin in a rubber based component of a pneumatic tyremay be determined by means of thermogravimetric analysis, abbreviated asTGA. HTC lignin begins to combust in lower temperatures than carbonblack which is conventionally used in rubber based compounds of apneumatic tyre. When performing a thermogravimetric analysis on a curedrubber based component, such as vulcanized rubber product, the componentis first treated by acetone, as described above.

A cured rubber based component comprising HTC lignin may undercombustible conditions produce a first derivative curve peak of thesecond mass change at a temperature equal to or less than 550° C. Athermogravimetric analysis of the cured rubber based component, afteracetone extraction treatment according to standard D297-93 (2006),produces a first derivative curve peak of the second mass change at atemperature equal to or less than 550° C., when the cured rubber basedcomponent is subjected to a thermogravimetric analysis in a temperaturerange between 20° C. and 800° C. at a heating rate of 10° C./minuteaccording to standard ASTM D6370-09. The first derivative TGA curve peakof the first mass change may be, for example, in a temperature in therange of 440 to 550° C. In comparison, a cured rubber based componentcomprising only carbon black typically has a first derivative TGA curvepeak of the first mass change at a higher temperature than a curedrubber based component comprising HTC lignin.

The amount of organics content in rubber based compound comprising HTClignin may be higher than the amount of organics content in rubber basedcompound comprising only conventional fillers, such as carbon blackand/or silica. The amount of residual mass, principally ash, remainingafter the thermogravimetric analysis, may be higher in a cured rubberbased components comprising HTC lignin than in conventional componentscomprising only carbon black. The residual matter of a cured rubberbased component comprising HTC lignin may be, for example, in the rangeof 2.5% to 10% by weight of the cured rubber based component.

Referring to FIGS. 14, 15, 16 and 17. TGA may be used to measure theamount and rate of change in the mass of a sample as a function oftemperature or time in a controlled atmosphere. FIGS. 14, 15 and 16 areTGA results illustrating the mass change of a rubber based componentafter acetone extraction treatment as described above, when the rubberbased component was heated at a constant rate of 10° C. per minute, overa temperature range from 20° C. to 800° C., according to standard ASTMD6370-09. The instrument used was Netzsch TG 209 F1 Libra, with Proteussoftware. FIG. 17 is a TGA result illustrating the mass change of HTClignin, when analyzed in the same manner. The atmosphere profile in eachanalysis was N₂/O₂/N₂/N₂. The crucible in each analysis was of aluminumoxide (Al₂O₃). The vertical axis on the left side of each diagramrepresents the mass change in percentages (TG/%). The vertical axis onthe right side of each diagram represents the differential mass change(DTG/(%/min)). The horizontal axis of each diagram represents the timein minutes. The continuous line in each diagram is a thermogravimetriccurve, illustrating the sample mass versus time. The dashed line in eachdiagram is the differential thermogravimetric curve, referred to also asthe first derivative TGA curve, illustrating the rate of sample massloss versus time. The first mass change in each diagram, between timeperiod ranging from 0 to 85 minutes, represents the organics content ofthe sample remaining after the acetone extraction treatment. The secondmass change in each diagram, between time period ranging from 85 to 138minutes, represents the combustion of carbon black with oxygen. Theresidual mass in each diagram represents the ash content of the sample,wherein the ash content may comprise for example zinc oxide and/orsilica. Around 90 minutes time point, when the atmosphere of the TGAcontains oxygen, minor increases in sample mass may be detected due tooxidation reactions in the samples. Such increases in sample masstypically indicate the presence of metals which may be oxidized.

FIG. 14 discloses TGA results of a sample of cured rubber basedcomponent comprising 46 phr of lignin that had not been treated byhydrothermal carbonization and corresponded to the reference sample CMP1of the FTIR analysis. The initial sample mass was approximately 14.5milligrams, referring to the mass at the beginning of the TGA analysis.The TGA results show that the sample containing lignin undergoes a firstmass change, wherein 89.96% of the sample mass is lost. The samplecontaining lignin has a first derivative TGA curve peak of the firstmass change at a time point of 44.2 minutes, at a temperature of 446.5°C. The TGA results further show that the sample containing lignin thenundergoes a second mass change under atmosphere containing oxygen,wherein 7.44% of the sample mass is lost. The sample containing ligninhas a first derivative TGA curve peak of the second mass change at atime point of 104.7 minutes, at a temperature of 472.0° C. The samplecontaining lignin has a residual mass of 2.31%.

FIG. 15 discloses TGA results of a sample of cured rubber basedcomponent comprising 46 phr of N660 grade carbon black, and correspondedto the reference sample CMP3 of the FTIR analysis. The initial samplemass was approximately 14.4 milligrams, referring to the mass at thebeginning of the TGA analysis. The TGA results show that the samplecontaining carbon black undergoes a first mass change, wherein 69.96% ofthe sample mass is lost. The sample containing carbon black has a firstderivative TGA curve peak of the first mass change at a time point of45.4 minutes, at a temperature of 458.6° C. The TGA results further showthat the sample containing carbon black then undergoes a second masschange under atmosphere containing oxygen, wherein 27.62% of the samplemass is lost. The sample containing carbon black has a first derivativeTGA curve peak of the second mass change at a time point of 121.1minutes, at a temperature of 635.5° C. The sample containing carbonblack has a residual mass of 2.19%.

FIG. 16 discloses TGA results of a sample of cured rubber basedcomponent comprising 46 phr of HTC lignin, referring to lignin that hadbeen treated by hydrothermal carbonization, and corresponded to thesample CMP2 of the FTIR analysis. The initial sample mass wasapproximately 14.5 milligrams, referring to the mass at the beginning ofthe TGA analysis. The TGA results show that the sample containing HTClignin undergoes a first mass change, wherein 81.29% of the sample massis lost. The sample containing HTC lignin has a first derivative TGAcurve peak of the first mass change at a time point of 44.6 minutes, ata temperature of 450.5° C. The TGA results further show that the samplecontaining HTC lignin then undergoes a second mass change underatmosphere containing oxygen, wherein 14.77% of the sample mass is lost.The sample containing HTC lignin has a first derivative TGA curve peakof the second mass change at a time point of 99.5 minutes, at atemperature of 420.3° C. The sample containing HTC lignin has a residualmass of 3.64%.

FIG. 17 discloses TGA results of a sample of HTC lignin, referring tolignin that had been treated by hydrothermal carbonization, which may bemixed with a rubber to manufacture a rubber based component for apneumatic tyre. The initial sample mass was approximately 11.7milligrams, referring to the mass at the beginning of the analysis. TheTGA results show that the sample containing HTC lignin undergoes a firstmass change, wherein 40.03% of the sample mass is lost. The samplecontaining HTC lignin has a first derivative TGA curve peak of the firstmass change at a time point of 38.0 minutes, at a temperature of 370.1°C. The TGA results further show that the sample containing HTC ligninthen undergoes a second mass change under atmosphere containing oxygen,wherein 58.61% of the sample mass is lost. The sample containing HTClignin has a first derivative TGA curve peak of the second mass changeat a time point of 96.4 minutes, at a temperature of 403.7° C. Thesample containing HTC lignin has a residual mass of 1.23%.

A Method for Determining the Specific Surface Area of HTC Lignin from aCured Rubber Based Component of a Pneumatic Tyre

The specific surface area may be determined according to ASTM D6556-10,the specific surface area referring to the total surface area based onmultipoint nitrogen adsorption, denoted as NSA. The NSA is based on theB.E.T theory, which includes the total surface area, inclusive ofmicropores with pore diameters less than 2 nm (20 Å). Specific surfacearea based on multipoint nitrogen adsorption is widely used fordetermining the total and external surface area of carbon black andcarbon black type material. HTC lignin in this context refers to carbonblack type material.

In general, HTC lignin suitable for a rubber based component of apneumatic tyre may have a specific surface area of less than 150 m²/g,when measured according to ASTM D-6556-10 from material which has notbeen mixed with rubber, referred to as virgin material.

The specific surface area of HTC lignin suitable for a rubber basedcomponent of a pneumatic tyre is different, when measured from a curedrubber based component of a pneumatic tyre. The specific surface area ofHTC lignin may be measured from a sample of cured rubber based componentaccording to the same standard (ASTM D6556-10). The method fordetermining the specific surface area of HTC lignin comprises separatingthe filler material comprising carbon black and/or HTC lignin from thecured rubber based component. Rapra Review Reports (Rubber Analysis:Polymers, Compounds and Products, Volume 12, Number 7, 2001 p. 22)discloses a method suitable for separation of carbon black type materialfrom a cured rubber based component. A pyrolysed HTC lignin in thiscontext refers to carbon black type material. The method disclosed inthe literature is modified in that the pyrolysis of the sample isperformed at 600° C., thereby converting the sample to a pyrolysisproduct. The specific surface area is measured from the separated carbonblack type material of the pyrolysis product according to the samestandard (ASTM D6556-10). During pyrolysis at 600° C., the samplecomprising HTC lignin may undergo further decomposition of HTC lignin,thereby leading to increased specific surface area of the sample. Thespecific surface area of such pyrolysis product is considerably higherthan the specific surface area of virgin HTC lignin material, which hasnot been mixed with rubber.

A cured rubber based component comprising HTC lignin, when pyrolysed at600° C. may be converted to a pyrolysis product having a specificsurface area of equal to or higher than 200 m²/g. The specific surfacearea of the pyrolysis product may be equal to or higher than 300 m²/g,even equal to or higher than 400 m²/g. The specific surface area of thepyrolysis product may be, for example, in the range of 200 to 400 m²/g,or in the range of 300 to 400 m²/g. Such high specific surface areas arecharacteristic to cured rubber based component comprising lignin thathas been treated by hydrothermal carbonization. The increase of surfacearea has not been observed when pyrolysing samples containing onlycarbon black, which makes this a distinguishing feature of cured rubberbased component comprising HTC lignin.

The cured rubber based component of a pneumatic tyre comprising HTClignin, when pyrolysed at 600° C., may thus be converted to a pyrolysisproduct, wherein the carbon black type filler material, once separatedfrom the pyrolysis product, may have a specific surface area of equal toor higher than 200 m²/g, when determined according to ASTM D6556-10, thespecific surface area referring to the total surface area based onmultipoint nitrogen adsorption, the carbon black type filler materialreferring to carbon black and/or HTC lignin.

Rolling Resistance of a Pneumatic Tyre Comprising HTC Lignin

A rubber based component has both elastic and viscous qualities. Rollingresistance of a tyre is typically characterized by tangent delta,abbreviated as tan δ. Tangent delta is a ratio of the loss modulus tothe storage modulus. Storage modulus measures the stored energy,representing the elastic portion.

Loss modulus measures the energy dissipated as heat, representing theviscous portion. Tangent delta relates to the processability of rubberbased component in uncured state. Tangent delta relates to the heatgeneration, known as hysteresis, of a cured rubber based component ofpneumatic tyre. A lower tangent delta value reflects reduced heatgeneration characteristics of a material.

Tangent delta relates inversely to the resiliency of a cured rubberbased component of pneumatic tyre. Components with a higher modulus aremore resilient. A resilient material comprises less flexing fatigue.Resiliency of a tyre may be measured by a 300% modulus test, which is ameasure of tensile strength at a particular elongation. In other words,the 300% modulus of a tyre is a measure of the stress required toproduce 300% elongation in a uniaxial tension test. Tangent delta may bedetermined by dynamic mechanical analysis, known as DMA. 300% modulustest value may be determined by uniaxial tensile tester. Hereafter, the300% modulus test value is referred to as the modulus value, unlessotherwise stated.

Heat generation and flexing fatigue of a tyre may be measured accordingto ASTM D623-99. In a dynamic mechanical analysis a sinusoidal force(stress σ) is applied to a material and the resulting displacement(strain) is measured.

A pneumatic tyre comprising cured rubber based component comprising HTClignin may be configured to have characteristics, which reduce therolling resistance of the tyre. HTC lignin may be used in a rubber basedcomponent of a pneumatic tyre to decrease ratio of loss modulus tostorage modulus. Referring to the description of HTC lignin above, HTClignin may be used in a rubber based component of a pneumatic tyre withor without a coupling agent, such as a silane based coupling agent. HTClignin may be used in a non-tread area of a rubber based component of apneumatic tyre, such as a sidewall or bead area component. HTC ligninmay be used in a tread area of a rubber based component of a pneumatictyre.

The tangent delta of a cured rubber based component may be measured withdynamic thermomechanical analyzer, denoted as DTMA, for example at 10 Hzfrequency at a temperature in the range of 50° C. to 70° C., preferablyin a temperature of 60° C., which is commonly used for prediction ofrolling resistance of a tyre.

Effects of HTC lignin to the tangent delta and modulus values of apneumatic tyre are further illustrated below, by way of examples.

Referring to FIG. 18. Tangent delta value using DTMA with 10 Hzfrequency at 60° C. temperature was determined independently from threepneumatic tyre samples REF10, REF20, SMP10, each sample representing anon-tread area component, all samples having identical dimensions. Thesample SMP10 represented a cured rubber based component of a pneumatictyre comprising HTC lignin without a coupling agent. The amount of HTClignin in the cured rubber based component of a pneumatic tyre was 46phr. The first reference sample REF10 represented a cured rubber basedcomponent of a pneumatic tyre comprising carbon black. The amount ofcarbon black in the cured rubber based component of a pneumatic tyre was46 phr. The carbon black was of N660 grade, having a specific surfacearea in the range of 30 to 40 m²/g. The second reference sample REF20represented a cured rubber based component of a pneumatic tyrecomprising silica and a silane based coupling agent. The vertical axisin FIG. 18 represents relative value of tangent delta (tan δ) in eachsample. The values are are relative to the reference sample REF20, whichhas been given an index value of 100. A relative value higher than 100,in this context, represents a decrease in tangent delta (tan δ) value.Therefore, a higher relative value corresponds with a lower tangentdelta value. A lower tangent delta value in turn corresponds with alower rolling resistance. Sample SMP10 comprising HTC lignin has arelative value of 126. Reference sample REF10 comprising carbon blackhas a relative value of 77. Sample SMP10 comprising HTC lignin thereforehas a 26% lower tangent delta value than reference sample REF20comprising silica. Sample SMP10 comprising HTC lignin has a 64% lowertangent delta value than reference sample REF20 comprising carbon black.

Referring to FIG. 19. Tangent delta value using DTMA with 10 Hzfrequency at 60° C. temperature was determined independently from threepneumatic tyre samples REF11, REF21, SMP11, each sample representing anon-tread area component, all samples having identical dimensions. Thesample SMP11 represented a cured rubber based component of a pneumatictyre comprising HTC lignin and a silane based coupling agent. The amountof HTC lignin in the cured rubber based component of a pneumatic tyrewas 46 phr. The reference sample REF11 represented a cured rubber basedcomponent of a pneumatic tyre comprising 46 phr of carbon black. Thecarbon black was of N660 grade, having a specific surface area in therange of 30 to 40 m²/g. The reference sample REF21 represented a curedrubber based component of a pneumatic tyre comprising silica and asilane based coupling agent. The vertical axis in FIG. 19 represents therelative value of tangent delta (tan δ) in each sample. The values arerelative to the reference sample REF21, which has been given an indexvalue of 100, as above. Sample SMP11 comprising HTC lignin has arelative value of 118. Reference sample REF11 comprising carbon blackhas a relative value of 95. Sample SMP11 comprising HTC lignin and asilane based coupling agent has a 18% lower tangent delta value thanreference sample REF21 comprising silica and a silane based couplingagent. Sample SMP11 comprising HTC lignin and a silane based couplingagent has a 24% lower tangent delta value than reference sample REF21comprising carbon black.

The results demonstrate, that a cured rubber based component of apneumatic tyre comprising HTC lignin may have a tangent delta valuewhich is lower than the tangent delta value a cured rubber basedcomponent of a pneumatic tyre comprising carbon black or silica. Thetangent delta value of a cured rubber based component of a pneumatictyre comprising HTC lignin may be equal to or less than 18% of thetangent delta value of a cured rubber based component of a pneumatictyre comprising silica and/or carbon black. The tangent delta value acured rubber based component of a pneumatic tyre comprising HTC ligninmay be equal to or less than 25% of the tangent delta value of a curedrubber based component of a pneumatic tyre comprising silica and/orcarbon black. The tangent delta value of a cured rubber based componentof a pneumatic tyre comprising HTC lignin may be up to 64% lower thanthe tangent delta value of a cured rubber based component of a pneumatictyre comprising silica and/or carbon black.

The tangent delta of a cured rubber based component of a pneumatic tyrecomprising HTC lignin may be denoted as tan δ_(HTC1). The tangent deltaof a cured rubber based component of a pneumatic tyre comprising HTClignin and a silane based coupling agent may be denoted as tan δ_(HTC2).The tangent delta of a cured rubber based component of a pneumatic tyrecomprising carbon black may be denoted as tan δ_(CB). The tangent deltaof a cured rubber based component of a pneumatic tyre comprising silicamay be denoted as tan δ_(SI).

According to an embodiment, tan δ_(HTC1) may be at least 5% lower thantan δ_(CB). The tan δ_(HTC1) may be at least 10% lower than tan δ_(CB),such as at least 20% lower than tan δ_(CB). The ratio tan δ_(HTC1)/tanδ_(CB) may be, for example, in the range of 0.95 to 0.6.

According to an embodiment, tan δ_(HTC2) may be at least 5% lower thantan δ_(CB). The tan δ_(HTC2) may be at least 10% lower than tan δ_(CB),such as at least 20% lower than tan δ_(CB). The ratio tan δ_(HTC2)/tanδ_(CB) may be, for example, in the range of 0.95 to 0.8.

Referring to FIG. 20. The tensile strength required to produce a 300%elongation was measured by the 300% modulus test. The modulus value,referring to the value of the 300% modulus test, was determined withuniaxial tensile tester independently of four pneumatic tyre samplesREF12, REF22, SMP32, REF32, each sample representing a non-tread areacomponent, all samples having identical dimensions. The sample SMP32represented a cured rubber based component of a pneumatic tyrecomprising 46 phr of HTC lignin. The cured rubber based component of apneumatic tyre comprised HTC lignin and a silane based coupling agent.The reference sample REF12 represented a cured rubber based component ofa pneumatic tyre comprising 46 phr of carbon black. The carbon black wasof N660 grade, having a specific surface area in the range of 30 to 40m²/g. The reference sample REF22 represented a cured rubber basedcomponent of a pneumatic tyre comprising silica and a silane basedcoupling agent. The reference sample REF32 represented a cured rubberbased component of a pneumatic tyre comprising 46 phr of lignin and asilane based coupling agent, wherein the lignin had not been treated byhydrothermal carbonization. The vertical axis in FIG. 20 represents therelative modulus value, which refers to the relative tensile strengthrequired to produce a 300% elongation in a sample. A relative modulusvalue higher than 100, in this context, represents a higher tensilestrength required to produce a 300% elongation in a sample. A highertensile strength in turn corresponds with increased resiliency. Thevalues are relative to the reference sample REF12 comprising carbonblack, which has been given an index value of 100. The reference sampleREF22 comprising silica has a relative value of 112. Sample SMP32comprising HTC lignin has a relative value of 114. The reference sampleREF32 comprising lignin had not been treated by hydrothermalcarbonization has a relative value of 53. Sample SMP32 comprising HTClignin and a silane based coupling agent has a 14% higher modulus 300%value than reference sample REF12 comprising carbon black. Sample SMP32comprising HTC lignin and a silane based coupling agent has a 2% highermodulus 300% value than reference sample REF22 comprising silica and asilane based coupling agent. Sample SMP32 comprising HTC lignin and asilane based coupling agent has a 216% higher modulus 300% value thanreference sample REF32 comprising lignin and a silane based couplingagent, wherein the lignin had not been treated by hydrothermalcarbonization.

The results demonstrate, that a cured rubber based component of apneumatic tyre comprising HTC lignin may have a modulus value which ishigher than the modulus value of a cured rubber based component of apneumatic tyre comprising carbon black or silica. The modulus value acured rubber based component of a pneumatic tyre comprising HTC ligninand a silane based coupling agent may be equal to or higher than themodulus value of a cured rubber based component of a pneumatic tyrecomprising silica. The modulus value a cured rubber based component of apneumatic tyre comprising HTC lignin and a silane based coupling agentmay be equal to or higher than 14% of the modulus value of a curedrubber based component of a pneumatic tyre comprising carbon black. Themodulus value a cured rubber based component of a pneumatic tyrecomprising HTC lignin and a silane based coupling agent may be equal toor more than 200% of the modulus value of a cured rubber based componentof a pneumatic tyre comprising lignin and a silane based coupling agent,wherein the lignin has not been treated by hydrothermal carbonization.

The modulus value of a cured rubber based component of a pneumatic tyrecomprising HTC lignin and a silane based coupling agent may be denotedmay be denoted as MOD_(HTC2). The modulus value of a cured rubber basedcomponent of a pneumatic tyre comprising carbon black may be denoted asMOD_(CB). The modulus value of a cured rubber based component of apneumatic tyre comprising silica may be denoted as MOD_(SI). The modulusvalue of a cured rubber based component of a pneumatic tyre comprisinglignin and a silane based coupling agent, wherein the lignin has notbeen treated by hydrothermal carbonization may be denoted as MOD_(LIG).

According to an embodiment, MOD_(HTC2) may be at least 5% higher thanMOD_(CB). The MOD_(HTC2) may be at least 10% higher than MOD_(CB), suchas at least 14% higher than MOD_(CB). The ratio MOD_(HTC2)/MOD_(CB) maybe, for example, in the range of 1.05 to 1.14 or higher.

According to an embodiment, MOD_(HTC2) may be equal to or higher thanMOD_(SI). The MOD_(HTC2) may be at least 2% higher than MOD_(SI). Theratio MOD_(HTC2)/MOD_(SI) may be, for example, in the range of 1.00 to1.02 or higher.

According to an embodiment, MOD_(HTC2) may be at least 100% higher thanMOD_(LIG). The MOD_(HTC2) may be at least 200% higher than MOD_(CB),such as at least 216% higher than MOD_(CB). The ratioMOD_(HTC2)/MOD_(CB) may be, for example, in the range of 1.50 to 2.16 orhigher.

The results demonstrate that when carbon black is replaced by HTC ligninin a non-tread area component of a pneumatic tyre, such as sidewall orbead area component, the rolling resistance of the pneumatic tyre maydecrease. The results further demonstrate that when silica is replacedby HTC lignin in a non-tread area component of a pneumatic tyre, such assidewall or bead area component, the rolling resistance of the pneumatictyre may decrease. The results demonstrate that use of HTC lignin mayreduce the rolling resistance of a pneumatic tyre, when used with asilane based coupling agent. The results demonstrate that use of HTClignin may reduce the rolling resistance of a pneumatic tyre even more,when used without a coupling agent. The amount of carbon black replacedby HTC lignin may be, for example equal to or higher than 75 wt. %, suchas in the range of 1 to 70 wt. %, preferably in the range of 20 to 60wt. %, and most preferably in the range of 30 to 50 wt. % of the weightof the carbon black.

The above-listed examples and embodiments illustrate non-limitingexamples. The amounts of HTC lignin disclosed in the above-listedexamples may be varied. HTC lignin amounts in a rubber based componentof a pneumatic tyre A rubber based component of a pneumatic tyre maycomprise HTC lignin, for example, in an amount equal to or less than 46phr. A rubber based component of a pneumatic tyre may comprise HTClignin, for example, in an amount equal to or higher than 46 phr.

For the person skilled in the art, it will be clear that modificationsand variations of the pneumatic tyre and the method according to thepresent invention are perceivable. The figures are schematic. Thefigures are meant to be illustrative representations of exampleembodiments of the invention. In particular, the FIGS. 1-6 are not inany particular scale. The abbreviation wt. % refers to weightpercentage, unless otherwise stated. The abbreviation phr refers toparts per hundred rubber, a term widely used in the rubber manufacturingindustry.

The particular embodiments described above with reference to theaccompanying drawings are illustrative only and not meant to limit thescope of the invention, which is defined by the appended claims.

The invention claimed is:
 1. A pneumatic tyre for a vehicle, the tyrecomprising a metal component, a textile component and a cured rubberbased component, the components bonded together by means of curing, andthe cured rubber based component comprising lignin that has been treatedby hydrothermal carbonization.
 2. The pneumatic tyre of claim 1, whereinthe cured rubber based component contains 2-methoxyphenol, the presenceof 2-methoxyphenol being determinable by means of Pyrolysis-GasChromatography/Mass Spectroscopy analysis from the cured rubber basedcomponent, when pyrolysed at 550° C. according to standard ASTMD3452-06.
 3. The pneumatic tyre according to claim 1, wherein the curedrubber based component, when pyrolysed at 600° C. according to standardASTM D3677-10, produces a pyrolysis product having an infraredspectrophotometry absorption band with a peak maximum around 1259 cm⁻¹.4. The pneumatic tyre according to claim 1, wherein the cured rubberbased component, when pyrolysed at 600° C., produces a pyrolysis producthaving a specific surface area of equal to or higher than 200 m²/g, thespecific surface area referring to total surface area based onmultipoint nitrogen adsorption according to ASTM D6556-10 of carbonblack type filler material separated from the pyrolysis product.
 5. Thepneumatic tyre according to claim 1, wherein the cured rubber basedcomponent, after an acetone extraction treatment according to standardD297-93, produces a first derivative curve peak of a second mass changeat a temperature equal to or less than 550° C., when the cured rubberbased component is subjected to a thermogravimetric analysis temperaturerange between 20° C. and 800° C. at a heating rate of 10° C./minuteaccording to standard ASTM D6370-09.
 6. The pneumatic tyre according toclaim 1, wherein the rubber based component comprises lignin that hasbeen treated by hydrothermal carbonization in an amount that is higherthan 0% but equal to or less than 75 wt. % of total weight of the rubberbased component.
 7. The pneumatic tyre of claim 6, wherein the rubberbased component comprises lignin that has been treated by hydrothermalcarbonization in an amount in a range of 10 to 70 wt. % of total weightof the rubber based component.
 8. The pneumatic tyre of claim 6, whereinthe rubber based component comprises lignin that has been treated byhydrothermal carbonization in an amount in a range of 20 to 60 wt. % oftotal weight of the rubber based component.
 9. The pneumatic tyreaccording to claim 1, wherein the rubber based component compriseslignin that has been treated by hydrothermal carbonization in an amounthigher than 0 wt. % but less than 10 wt. % of total weight of the rubberbased component.
 10. The pneumatic tyre of claim 9, wherein the rubberbased component comprises lignin that has been treated by hydrothermalcarbonization in an amount in the range of 0.5 to 9.5 wt. % of the totalweight of the rubber based component.
 11. The pneumatic tyre of claim 9,wherein the rubber based component comprises lignin that has beentreated by hydrothermal carbonization in an amount in a range of 2 to 9wt. % of the total weight of the rubber based component.
 12. Thepneumatic tyre according to claim 1, wherein the rubber based componentcomprises lignin that has been treated by hydrothermal carbonization,and methylene donor compound.
 13. The pneumatic tyre according to claim12, wherein the methylene donor compound is a polyamine based hardeningresin, selected from the group consisting of hexamethylenetetramine orhexa(methoxymethyl)melamine.
 14. The pneumatic tyre according to claim1, wherein the rubber based component further comprises a silane basedcoupling agent, the coupling agent being capable of bonding in achemical reaction with a rubber compound of a tyre.
 15. The pneumatictyre of claim 14, wherein the coupling agent isbis-[3-(triethoxysilyl)-propyl]-tetrasulfide.
 16. The pneumatic tyreaccording to claim 1, wherein the lignin that has been treated byhydrothermal carbonization comprises lignin of wooden origin.
 17. Thepneumatic tyre according to claim 1, wherein the rubber based componentis a non-tread area component or a tread area component.
 18. Thepneumatic tyre according to claim 17, wherein the non-tread areacomponent is a sidewall, or a bead area component.
 19. The pneumatictyre according to claim 18, wherein the bead area component is a clinch,or an apex.
 20. The pneumatic tyre according to claim 17, wherein thetread area component is a tread, a tread base, an undertread, or ashoulder.